Method of detecting gas in well drilling fluids



Nov. 22,1949 J. T. HAYWARD 2,489,180

METHOD OF bETBCTING GAS IN WELL-DRILLING FLUIDS Filed April 1, 1939 INVENTOR. .bhn 7. Haymrd A TTORNEYS.

Patented Nov. 22, 1949 UNITED STATES ATENT OFFICE.

METHOD or DETECTING GAS IN WELL one FLUIDS This invention relates to a method for detecting gas and particularly to a method for detecting and measuring combustible gas in hydraulic fluids employed in rotary well drilling.

In the drilling of oil or gas wells, wherein a hydraulic fluid such as a suspension of clay or earthy materials in water and called a mudladen fluid is circulated through the well during the drilling thereof, particularly by rotary drilling, by conventional practice, the specific gravity of the circulating fluid is controlled, ordinarily, so that the head of fluid in the well is greater than the pressure of oil or gas which it is expected will be encountered at points in the well. This procedure is followed in order to prevent the pressure of a gas formation, which may be encountered, from exceeding that of the fluid head pressure and-causing blow-outs," whereby the fluid is blown from the well with disastrous consequences which, in some cases, may result in complete construction of the well and endanger lives and property in the vicinity of the well.

While this procedure is advantageous for protecting the well during drilling, it is disadvantageous in that the excess pressure of the hydraulic fluid prevents the entrance into the well of gas from an encountered gas-containing formation, with the result that 'such formation may entirely escape detection of the drill operators and become mudded-ofi or sealed by the circulating mud fluid, and erroneously cause the well to become abandoned as a non-producer. Also, as oil is very often found in immediate or adjacent association with gas, failure to detect the presence of gas substantially immediately after penetration by the drill into the gas formation, may cause the driller to continue entirely through the oil-containing formation and also mud-off that formation. This is particularly true where, as is often the case, the oil-containing formation is quite thin, that is, only a few feet thick. The danger is heightened greatly by the fact that oil and gas formations are usually sandy formations, which are relatively soft and will be very quickly traversed by the drill unless comparatively exact knowledge of the location of such formations is known before-hand and the approach of the drill thereto very carefully controlled.

Since as noted, the pressure of the fluid column in the well is ordinarily controlled to exceed that of any gas formation which may be encountered, only that relatively small quantity of gas, which is contained in the core, i. e., the relatively traversing the formation, will escape into the fluid, and recognition of the gas formation must rely wholly upon the prompt detection of this small quantity of gas in the fluid. The following example will serve to illustrate the relatively minute quantities of gas which will be present in the mud fluid under a normal set of drilling conditions: A well is being drilled at a depth of 6000 feet where a gas-containing formation is encountered. The formation pressure is approximately 3000 pounds per square inch. The mud fluid in the well has a specific gravity of 1.38 producing a fluid column pressure at the bottom of the well of approximately 3600 pounds per square inch or approximately 600 pounds per square inch greater than that of the gas formation. 0bviously under these conditions, substantially no gas will escape into the well from the gas formation and the only gas entering the circulating fluid will be that relatively small amount of gas present in the cuttings comprising the core or cylinder of the formation being cut out by the drill bit. Assume the diameter of the bore of the well is nine inches, a conventional size. The volume of each lineal foot of the cylinder of gas formation drilled will be approximately 763 cubic inches. If we assume a porosity of :25 per cent, that is, the pore space in the formation in which the gas is held constitutes 25 percent of the volume of the formation, then it is evident that the total volume of gas in one lineal foot of the cylinder of formation will be approximately 191 cubic inches at a pressure of 3000 pounds per square inch. When the fluid containing this quantity of gas reaches the surface of the ground, the pressure will be reduced to substantially atmospheric pressure, and disregarding the factor of temperature, the gas will expand roughly 200 times its previous volume, or to a volume of 38,200 cubic inches. However, as the mud fluid is ordinarily circulated through the well at a rate of approximately 100 barrels per lineal foot drilled, the 38,200 cubic inches of gas will be distributed through 100 barrels of mud fluid,'and upon calculation, it will be found that the mud fluid, when it reaches the top of the well, will contain only about 3.9% by volume of gas. Such a small quantity of gas is practically impossible to detect by ordinary inspection methods, due to the fact that the mud fluids ordinarily used in drilling are generally very viscous and have gel-like properties which cause the minute globules of gas to be strongly occluded in the fluid to an extent, in many cases, that substantially none of the gas small cylinder of formation cut out by the drill will escape from the fluid, even when the fluid Generally stated, and in accordance with this Other objects and advantages of this invention will be apparent from the following detailed description taken in conjunction with the accompany-ing drawing which illustrates, more or less, diagrammatically, an arrangement of apparatus which is adapted for successfully performing the method of this invention.

Referring to the drawing, the numeral I designates a section of the ordinary surface casing invention, the method of detecting gas which has become dilutedly occluded in the circulating mud-laden fluid employed in the drillingof an oil or gas well by the drilling of a stratum while the fluid column is maintained at a head exceedingthe head of the stratum, comprises, causing separation of and collecting gas from the drilling fluid at the top of the well, as the drilling proceeds, in amounts sufllcient for analysis, and making analyses of the gas. Preferably, gas portions are collected from successive portions of the drilling fluid, and the percentages of the gas in successive portions are determined. The release of the gas is caused at a rate sufllcient for continuous analyses, so that a continuous analysis of the collected gas is made. In accordance with an embodiment of this invention, the gas is separated from the fluid by applyin a as releasing force to the fluid as by passing air over the fluid. v

In accordance with an illustrative embodiment of this invention the dilutedly dispersed gas from a flowing stream of hydraulic fluid, such as well drilling fluids, is mixed with a volume of air which is continuously proportioned to the volume of gas evolved so as to provide a known constant volume of the resulting mixture of gaseous fluids, which is then analyzed, preferably by the well known hot filament method, to determine the percentage of gas in the mixture. The method is preferably applied by flowing the hydraulic fluid through a closed collecting zone to which the vacuum is applied, and admitting the air to the collecting zone through an orifice under the control of the vacuum applied. Thus as the volume of gas evolved changes, the volume of air drawn into the collecting zone will change proportionally so as to provide a constant volume of gas-air mixture in the collecting zone. By continuously withdrawing a constant volume mixture of gaseous fluid from the collecting zone, which is ordinarily effected through a flow meter by the suction applied to produce the vacuum in the collecting zone, the change in the relative proportion of gas in the gaseous fluid can be continuously determined by analysis, and this provides a measure of the rate of evolution of the gas from the hydraulic fluid, whereby the operators will be is to provide a method of detecting gas, which has become dilutedly occluded in the circulating extending into a well which is being drilled by the .well known rotary method. A hollow drill pipe 2 extends axially of the casing to the bottom of the well turning the usualdrill bit, not shown, in the conventional manner. Hydraulic fluid 3, such as a mud slurry commonly employed in such well drilling and which is ordinarily of such speciflc gravity as to maintain a fluid pressure in the well bore greater than the pressures in the travpipe 2 to the bottom of the well where it picks up the cuttings produced there by the action of the drill bit and carries such cuttings together with any naturally contained gas or other fluids upward toward the surface of the'ground through the annular space between the drill pipe 1 and the bore of the well, thence through the annular spaces between the drill pipe and the inner wall of surface casing I whence the hydraulic fluid cuttings and contained fluids. are discharged through a fluid discharge pipe 4 through which the mud fluids and cuttings are conveyed to the usual settling pits, not shown, and thence back to the suction of the conventional fluid circulating pump, also not shown. The portions of the apparatus described but not shown are well known and their functions well understood by those skilled in the art, and, therefore are not further elaborated or illustrated.

A gate 5 is hingedly mounted at 5 in conduit 4 at a point spaced some distance from the point where conduit 4 connects to casing I and is provided at its upper end with an angularly extending arm I on which is mounted a movable counterbalance 8. By suitable adjustment of counterbalance 8 on arm I, gate 5 is automatically mud-laden fluid employed in the drilling of an oil adapted to be held normally closed or partially closed against the flow of hydraulic fluid through conduit 4 and to thereby maintain the portion of the conduit between casing I and gate 5 substantially full of hydraulic fluid at all times. The portion of conduit between casing I and gate 5 is designated liquid seal trap 9.

A hollow gas collecting chamber Ill constructed of metal or other suitable rigid material and open at its lower end is connected into the upper surface of conduit 4 between casing I and gate 5. The open lower end of chamber III being in open communication with the interior of the conduit. The connection between chamber III and conduit 4 is made air tight to prevent entrance of uncontrolled extraneous air into the chamber.

An orifice tube I I of fixed area is positioned in the side of chamber II! at a point above the normal level of liquid in trap 9 and chamber III. A tube I2 has one end connected to the upper end of chamber In in communication with the interior thereof, and has its other end connected to a dilution orifice chamber I3, which is provided with a replacable orifice tube Il in one wall thereof, and with an outlet pipe IS in another wall thereof. Outlet pipe I5 leads through a meter I6 into a gas detector I9, which is prefer ably of the electric hot filament type of well known design commonly employed for detecting small amounts of combustible gases in air. Detector I9 is preferably provided with an indicating meter 20 which indicates the percentage of gas in the gaseous fluids passing through the detector. It will be understood that indicating member III may be of the recording type so as to provide a continuous record of the percentage of gas in the gaseous fluid being analyzed. Conduit I5 extends through detector I9 and connects to a vacuum pump II, which functions to draw gaseous fluids from chamber Ill through tube I2, orifice chamber I3, pipe I5, meter I 6 and detector It; the gaseous fluid thus drawn through this apparatus being discharged to the air through pipe l8. Since a hot filament detector of the type described is operative generally only with very small amounts ofgaseous fluids, a pipe 20A fitted with a valve 2I is provided to by-pass fluid passing through pipe I5 around detector I9 and into the suction of vacuum pump IT. A pipe 22 fitted with a valve 23 is connected into pipe I5 on the suction side of vacuum pump IT to provide means for regulating the vacuum applied by the pump.

A valved by-pass connection 24 is provided between tube I2 and outlet pipe I5 in order to permit routing of gaseous fiuld flowing from chamber In around dilution orifice chamber I3, since such dilution orifice is generally required only in connection with those types of gas detectors which are operative for detecting only very small concentrations of combustible gases in air. Where other types of detectors are employed, the dilution orifice chamber I3 need not be used. A vacuum gauge 25 is connected into pipe I5 for indicating the pressure in the apparatus ahead of meter I6. I

The above described apparatus is employed in the following manner:

Hydraulic well fluid, such as described above,

and containing well cuttings and hydrocarbon gas emerges from the top of the well and overflows from casing I through conduit 4 where it flows through liquid seal trap 9 on its way to the settling pits and circulating pumps. As the fluid passes through liquid seal trap 9, it will pass under the open end of chamber III in which a slight vacuum is maintained by means of vacuum pump I1. Gas evolving from the fluid, the evo lution of gas being assisted by the reduced pressure in chamber I II, will enter chamber I0. At the same time, by virtue of the reduced pressure, a quantity of air will be drawn into chamber -I through orifice tube II. The vacuum maintained in chamber I0 is so regulated by means of valve 23 that the quantity of air entering chamber III will be sufliicent to continuously purge the portion of chamber III above orifice tube I I and the pipes and apparatus connecting the chamber to detector I9 of all the gas being continuously evolved from the hydraulic fluid. The total volume of gaseous fluid drawn through ,pipe I5 will be measuredby means of meter I6 and by holding the metered volume constant by the described pressure regulation, the volume of air drawn into chamber I0 through orifice tube II will be automatically adjusted in accordance with the volume of gas evolved from the hydraulic fluid, so that any changes in the rate of evolution of gas from the hydraulic fluid will be immediately reflected in the subsequent analysis in detector I9. By means of the described liquid seal arrangement provided for the open end of chamber II), no extraneous unknown quantities of air can enter the apparatus to improperly alter the analysis.

The mixture of air and gas produced in chamher III as described will be drawn therefrom under the suction applied by vacuum pump I1, through tube I2 then through dilution orifice chamber I3, where an additional quantity of air, proportioned to the mixture in accordance with the relative areas of orifice I4 and tube I2 and pipe I5, will be mixed with the air-gas mixture from chamber I0 to further dilute the mixture so that the concentration of the gas in the diluted mixture will be within the limits of the particular form of detector I9. This flnal mixture then passes through meter It to detector I9. Since hot filament detectors of the type referred to are operative only on relatively minute amounts of gaseous fiuid, about percent of the diluted mixture is ordinarily by-passed around the detector through pipe 20A and valve 2| to the suction of pump I1. The remaining 10 percent passes through the detector I9 and is analyzed therein in the usual way and the percentage of gas in the mixture indicated on meter 20. It will be understood, of course, that the detection and indicating apparatus may be compensated for the fixed dilution effected in dilution orifice chamber I3, so that the reading of meter 20 will give directly the percentage of gas in the mixture from chamber I0. Where a detector is used which does not require the extra dilution effected in orifice chamber I3, this portion of the apparatus may be by-passed by closing the by-pass valves in tube I2 and pipe I5, opening the valve in b y-pass 24 and routing the gas-air mixture through by-pass 24 directly tometer I6.

The step of introducing air into chamber III, as by the orifice II in an amount sufllcient to continuously purge the chamber and connecting pipes is very important in assuring that changes in the rate of evolution of gas from the hydraulic fluid will be immediately and accurately detected in detector I9.

If no air were introduced in chamber In with the orifice chamber I3 omitted, then only pure gas would be drawn through the apparatus and there would then be no way of discovering a change in the rate of evolution of the gas. On the other hand, if a variable or unknown quantity of air were allowed to enter chamber I0, the percentages of gas determined by detector I9 would be meaningless. Again, if less air than is sufficient to completely and continuously purge chamber It was introduced therein, excessive percentages of gas would be indicated by detector I9 and would, therefore, be meaningless.

Therefore, by regulating the introduction of air into chamber II) in the manner described, to

maintain a constant flow of air-gas mixture through the chamber and connecting pipes and In an amount suflicient to keep these portions of the apparatus continuously purged, the changes in the quantity of gas evolved from the hydraulic fluid will appear directlyin the analysis. At the same time, by adding air to the evolved gas, a suflicient volume of gaseous fluid will be provided to bring the gas, immediately after its escape from the mud fluid, to the detection apparatus, otherwise, when the quantities of gas are small, substantial intervals of time may elapse before the gas can flow from chamber ID to the detection apparatus. Of course, when no gas is present in the drilling fluid, only air will be passing through detector I9 and no gas indication will appear therein.

It will be evident, therefore, from the foregoing, that a novel method has been disclosed for continuously detecting the presence of gas in drilling fluid and for continuously detecting changes in the quantity of gas in the drilling fluid during the drilling of a well. a

It will be understood that numerous changes may be made in the details of the apparatus described and illustrated. Various modifications of the liquid sealed gas trap, orifices and valves may also be used, all without departing from the scope of the appended claims.

By circulating a measured volume of hydraulic fluid through the well as 'a measured rate, this method of gas detection may be employed to locate the sub-surface strata from which the gas comes, and the well logged in this manner. Such a logging method is disclosed in my 'co-pending application Serial No. 187,619, flied January 29, 1937, which is now Patent 2,214,674, for a Method of logging wells.

It will also be understood, that the described method for detecting gas may be applied to the hydraulic fluids, both as such fluids enter and as they leave the well and any changes in gas content of the fluid efl'ected in the well may be determined by this method, by employing a correction factor based upon the volume of fluid flowing through the drill pipe and annular space between the drill pipe and the bore of the well. This comparison method is also described in detail in application Serial Number 187,619, referred to above.

While theories have been put forward, this has been done to facilitate the explanation, and it will be understood that this invention is not limited to any particular theory. It will also be understood that the invention is susceptible of various embodiments within the scope of the appended claims.

What I claim and desire to secure by Letters Patent is: v

1. The method or detecting gas which has become dilutedly occluded in the circulating mudladen fluid employed in the drilling of an oil or gas well by the drilling of a stratum while the fluid column is maintained at a head exceeding the head of the stratum, comprising, causing separation of and collecting gas from the drilling fluid at the top of the well, as the drilling proceeds, in amounts sufllcient for analysis and in accordance with increase of gas occluded in successive portions of the fluid and making comparative analyses of the collected gas in order to determine such increase.

2. The method of detecting gas which has become dilutedly occluded in the circulating mudladen fluid employed in the drilling of an oil or gas well by the drilling of a stratum while the fluid column is maintained at a head exceeding the head of the stratum, comprising, causing separation of and collecting gas portions from successive portions of the drilling fluid, as the I drilling proceeds, in amounts 'sufllcient for analysis and in accordance with increase of gas occluded in successive portions or the fluid and determining increases of the gas occluded in the successive portions.

3. The method oi detecting gas which has become dilutedly occluded in the circulating mudladen fluid employed in the drilling of an oil or gas well by the drilling of a stratum while the fluid column is maintained at a head exceedin the head of the stratum, comprising, applying a gas-releasing force to the drilling fluid at the top of the well, as the drilling proceeds, in order to with, and determining the increase of the gas evolved from successive portions.

4. The method of detectinggas which has become dilutedly occluded in the circulated mudladen fluid employed in the drilling of an oil or gas well by the drilling or a stratum while the fluid column is maintained at a head exceeding the head of the stratum, comprising, causing separation oi and collecting gas from the drilling fluid at the top of the well under atmospheric temperatures, as the drilling proceeds, in amounts sufficient for analysis, and making analyses ior the collected gas.

5. The method for detecting gas which has become dilutedly occluded in the circulating mudladen fluid employed in rotary well drilling while the fluid column is maintained at a head exceeding, the head 01' the stratum being drilled, which comprises, flowing a stream of the fluid through a collectingvzone, therein collecting gas evolved from said fluid in passage through said zone, mixing with the evolved gas in said zone a volume of air controllably proportioned to the volume or the evolved gas, withdrawing the resulting mixture oi gas and air from said zone, and making an analysis for the gas in said resulting mixure.

6. The method for; continuously detecting gas which has become dilutedly occluded in the circulating mud-laden fluid employed inrotary well drilling while the fluid column is maintained at a head exceeding the head of the stratum being drilled, which comprises, flowing a stream 6! the fluid leaving a well through a collecting zone, therein continuously collecting gas evolved from said fluid in passage through said zone, continuously mixing with the evolved gas in saidzone a volume of air controllably proportioned to the volume of the evolving gas, continuously withdrawing the resulting mixture of gas and air from said zone, and continuously determining the gas in said resulting mixture.

7. In the art of drilling wells by the rotary method, where a stream of drilling mud is circulated into and out of the well bore, the method of continuously determining the presence or absence of gas in'the returning mud as an indication of the penetration of a gas bearing formation which includes the steps oi, allowing the separation of gas from the stream of returning mud, and indicating to the operator that gas is separating.

8. The method of detecting gas which has become dilutedly occluded in the circulating mudladen fluid employed in the drilling of an oil or gas well by the drilling of a stratum while the fluid column is maintained at a head exceeding the head of the stratum, comprising, causing separation of gas from the drilling fluid at the top of the well, as the drilling proceeds, in amounts sufficient for analysis and in accordance with increase or decrease of gas occluded in successive portions of the drilling fluid, mixing the separated gas with air to provide a continuous and substantially unvarying flow of air-gas mixture in which the gas content varies in response to changes in the amount of gas separating from the drilling fluid, and making continuous quantitative determinations of the combustible gas content of said air-gas mixture.

9. The method of detecting gas which has bet causing separation of gas from the drilling fluid at the top of the well, as the drilling proceeds, in amounts sufllcient for analysis and in accordance with increase or decrease of gas occluded in suecessive portions of the drilling fluid, mixing the separated gas with air to provide a continuous 7 and substantially unvarying flow or air-gas mixture in which the gas content varies in response to changes in the amount of gas separating from the drilling fluid, subjecting a constant metered flow or the air-gas mixture to analysis for combustible gas, and making continuous quantitative determinations of the combustible gas content of said air-gas mixture.

JOHN T. HAYWARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Bhetter Nov. 15, 1881 Number 10 Number Name Date 977,970 Sawford Dec. 6, 1910 996,498 Mann June 27, 1911 1,057,631 Fowler Apr. 1, 1913 1,150,505 Diehl et al Aug. 17, 1915 1,680,334 Lewis et al Aug. 14, 1928 1,720,325 Hackstafl et al. July 9, 1929 1,843,878 Laubmeyer Feb, 2, 1932 1,847,884 Cross Mar. 1, 1932 1,999,147 Ambrose et al Apr. 23, 1935 2,082,329 Foran et a1. June 1, 1937 2,112,845 Howell Apr, 5, 1938 2,119,288 Raymond May 31, 1938 2,142,270 Vander Henst Jan. 3, 1939 2,152,439 Miller Mar. 28, 1939 2,195,898 Newton Apr. 2, 1940 2,214,674 Hayward Sept. 10, 1940 2,229,884 Chalkley Jan. .28, 1941 2,257,170 Howell Sept. 30, 1941 FOREIGN PATENTS Number Country Date 377,895 Great Britain Aug. 4, 1932 OTHER REFERENCES Oil-Field Exploration and Development, vol. II, by A. Beeby Thompson, published 1925 by Crosby, Lockwood and Son, London, pp. 687 and 727. 

